"hollering", as outlined in the Dean's memo, is fine. Attempting to execute a 'heckler's veto', however, is not.
The idea that it is some kind of "veto" is again to misattribute power to the powerless. This figurative and hyperbolic language ('veto', 'witch hunt', etc.) clouds judgment.
This isn't the UN security council. This is a lot of horrified young people attempting to find self-expression. Sometimes, it's messy.
FWIW I don't think there's much daylight between "hollering" and "heckling". "Protest is allowed but disruption is not allowed" is the (directly quoted) standard that the SLS Dean is attempting to enforce.